Transport properties of the non-Hermitian T-shaped quantum router

In this study, we design a T-shaped quantum router that comprises two-level systems (TLSs), an infinite coupled resonator waveguide (CRW), and a semi-infinite CRW. The loss (absorption) and gain (amplification) of the energy levels of the TLSs can be considered as energy exchange between the system and its environment. Considering loss in the ground state and gain in the excited state of the TLSs and loss of cavities, the system is non-energy-conserving and non-Hermitian. Loss in the system consists of loss of cavities and TLSs. The total transmission probabilities (TPs) of photons in the system are equal to 1 or lower when the system has loss only. Loss causes a bounce-back phenomenon in the TPs. The TPs have a divergent point when the TLSs have gain, and we obtain this divergent condition. The reflection probability has a minimal point only when photons are incident from the semi-infinite CRW and the system has loss. The TPs of the non-Hermitian router are increased by gain, decreased by loss, and conserved under certain conditions.